Bought this generator new a couple of years ago and always drained the gas or used stabil and ran every year multiple times. Finally go to use it, and when the unit is on full throttle it surges, runs smooth then drops down and surges back and does this ever other couple of seconds. If I choke it just a bit it will smooth out. I took the carb apart and did smell that old gas smell. I never paid a lof of attention to this unit, but I think it may have been doing it from day one. I cleaned all the areas and the main jet in the carbm but the issue still exists. I am not sure if the carb should be replaced, but it seems unlikely, the other issue is that I know mid year honda changed stuff in this model, and I have the firs rev of it. I know there is also an electric motor on the carb for thr thorttle, I am trying to find a service manual, but any ideas would be greatly appreciated.
There is an upright small pencil diameter sized fuel screen inside the fuel tank of the EU3000is. I went in through fuel filler opening on the the top of the unit with a tooth brush on a stick and cleaned the screen. I then siphoned the rust and dirt particles out of the tank. Doing it this way precludes the necessity of draining the tank. My 3000 has been working smoothly since. If the problem reoccurs, repeat the process.
Check the seals in the plastic idle jet
It sounds like the carbs are restricted and causing the engines to run lean. If applying the choke makes them run better this is a sure sign that the engine is starving for fuel. If you disassemble the carb and remove the main jet-you may still see a hole in the center but it may be restricted with varnish. I once disassembled the carb on a 4 wheeler at least a half dozen times before I compared the main jet with one that functioned well and realized that the hole was much smaller-lined with varnish!! If this might be the case, either purchase some new carb dip chemical and follow the directions or better yet, take it to a small engine or motorcycle shop and have them dip the jet-reinstall and hopefully your problem will be solved. Good luck.
Cleaning the carb bowl and jets in small engines.
Overnight I'll use coca cola as a fine cleaner and for more stubborn dirt use nitromoors paint stripper.
Coca cola's good at removing the build up on Jets whilst nitromoors will remove the gunge from the bootom of a float boal without having to scratch at it and ruin protective coatings.
Use WD40 with its red straw to blow through the passage ways to prove they are clear.
I own a very lightly used 3000is. I run it whenever I remember to give it a little exercise. Today at 35 degrees F it was running like bad unless I added a little choke. Reading over this thread and seeing all the conversation about fuel, I decided to drain the tank and put in a couple ounces of fresh stuff to see what would happen.
It\'s a miracle. Running like the $2500 sewing machine that it once was. Thanks guys and be sure to try this first. BTW, the fuel I removed was about 6 months old and bought in the summer.
Though fuel stabilizer is a great idea in the short term, it has a limited lifespan. Looking at the bottle of Honda's own fuel stabilizer it states"1/2 oz per gallon to stabilize fuel for 6 months". Beyond that, the good things in fuel can still evaporate off leaving that stinky varnish goo behind. Fuel these days also has a lower shelf-life than in days gone by. Drain the carb for long term storage. A full tank with stabilized fuel will be fine for much longer than the carb would.
An engine that surges at idle is not yet taking fuel from the main jet. Many people don't know about the pilot jet up on the top side of the carb. It has a very tiny orifice, and the tiny ones plug up fastest. It is a black plastic part that is usually held in place by an o-ring and prevented from popping up by the throttle-stop screw. This needs to be cleared, but be gentle because it isn't difficult to enlarge the size of the orifice.
Everything else the others have mentioned here makes sense. I find that Honda's Carburetor/Combustion Chamber cleaner is a great product for soaking fuel-varnished parts, then follow with compressed air or brake clean.
Also, I recommend highly recommend connecting a Battery Tender or other smart charger to the battery while the unit is in storage. Don't make the mistake of using a cheap "trickle charger" for long term. Although they work for periodic short charges, most of these will continue charging the battery even after it is fully charged, causing damage if left unattended. Smart chargers will go into a "float mode" when the battery reaches 100% and charge again when it drops down. Smart Chargers are cheaper than batteries!
It can be a problem of the wind vane ? of the govenor or ? its called i dont know but its function on the airflow allways adjust in combination with the air filter Replace first place the airfilter and use it always WITH FILTER in the trimming process the wind vane adjust the control knob on the carburetor it must be stable, on the other side can also be adjusted for the rpm hights while the required number of revolutions are the maximum voltage, this should not be too high, succeed not to get the vane stable than it could be that you do need to replace a new spring kit.
So air filter and springs kit for the wind vane this must be remedied in some other case because of the drop down and surge back in the question a little bit difficult to explain but here is what i mean.
How To Adjust The RPM On Honda GX390 Generator Engine
Do not overlook checking the throttle governor linkage tensioner spring. If it's weak or broken it will cause the engine to pulsate. You can also check the pulsating condition by stabilizing the governor linkage with your finger and see if the pulsating stops. That points to a bad spring.
The automatic throttle system increase the surging because it tries to compensate for the low revs. The bad fuel or carb blockage lowers the revs where the auto system increases them and hence the surges. Air in the carb can also do the same thing and it gets sucked in through weak gaskets or loose carb fittings.
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I have the same problem with the same generator. I never have had to use it in an emergency (no power at the house), but bought it just in case 2 summers ago which makes it about 1 1/2 years old. When I brought it home, I Stabilized the gas big time, (same as my motorcycle which I have never had a problem with since 1990), and today I went out to check the generator over. And the battery was flat which I expected, a few pulls on the recoil starter cord and she fired up OK. Then I could see the surging issue. When the switch is in the non-eco mode, it is not too bad but noticeable, when the eco switch is turned on to drop the engine RPM it becomes a real issue. The RPM drops just about what I'd say is a stall speed, and then catches up for a few beats and then drops back off again. I added some more Sta-Bil to the gas, and a dollop of carb cleaner-fuel injector cleaner. After she ran for a few more minutes, it was not too too bad. It was only about 15 degrees out, I was getting chilly and maybe high from fumes so shut her down as is. I, as a New Years resolution will go out and start it up more frequently to see what happens.
I have the eu3000is with the control motor on the carb as well for eco mode. Took the little motor off spun it a few times reinstalled and presto allacadabra away we went. Stopped the surging when trying to pick up a load. The control motor only rotates a few degrees. My guess flat spot or dirty contacts. We use this unit off grid and this is the first trouble in four years.
I think it's pretty well covered here, just a plug for bad gas, we see a lot of it, also the idle jets are real small and plug, making them surge. Use ethanol free fuel if possible, stabil is essential, and make sure it is fresh, not two years old!
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